How efficient is my light source?
Lumens per Watt is the best way to measure the efficacy of a light source.
As a comparative guide:
Candle = 0.3lm/W
HPL+ tungsten halogen lamp = 14,900lm/575W = 26lm/W - 400hr
CP82 tungsten halogen lamp = 13,500lm/500W = 27lm/W - 150hr
MSR575 HR discharge lamp = 40,000lm/575W = 85lm/W - 1,000hr
Fluorescent T8 lamp = up to 100lm/W - 18,000hr
Luxeon Rebel LED 5,700K white at 350mA = 100lm/W - not quoted
Luxeon Rebel LED 5,700K white at 700mA = 80lm/W - 50,000hr L70
The design and cleanliness of all optical elements: lenses, coatings, filters and reflectors will factor in the efficacy of a lighting fixture. The efficacy of the power supply and electronics are also an important factor. The above information is ONLY provided as a guide to the actual lamp or light source.
Is my light source fit for purpose?
Additional consideration should also be given to the relevance of the light source in relation to purpose. For example, it is now recognised that full spectrum lighting improves driver reaction times and changing light sources from low CRI to high CRI can reduce accidents. Alternatively safety levels can be preserved with less power if high CRI sources are used for street lighting.